Method and device for spatial charged particle bunching

ABSTRACT

A charged particle buncher includes a series of spaced apart electrodes arranged to generate a shaped electric field. The series includes a first electrode, a last electrode and one or more intermediate electrodes. The charged particle buncher includes a waveform device attached to the electrodes and configured to apply a periodic potential waveform to each electrode independently in a manner so as to form a quasi-electrostatic time varying potential gradient between adjacent electrodes and to cause spatial distribution of charged particles that form a plurality of nodes and antinodes. The nodes have a charged particle density and the antinodes have substantially no charged particle density, and the nodes and the antinodes are formed from a charged particle beam configured to hit the target.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.17/222,756 filed Apr. 5, 2021, which is a continuation of U.S.application No. 16/532,368, filed Aug. 5, 2019, which is a continuationof U.S. application Ser. No. 12/459,478, filed Jun. 30, 2009, whichclaims priority under 35 U.S.C. § 119(e) to U.S. Provisional Appl. No.61/133,604, filed Jun. 30, 2008, entitled “METHOD AND DEVICE FOR SPATIALCHARGED PARTICLE BUNCHING,” which is incorporated herein by reference inits entirety.

BACKGROUND Field

The present application relates to charged particle beams. Morespecifically, the present application relates to methods and apparatusesfor spatial charged particle bunching.

Description of the Related Art

Photolithography has been a key patterning step in most integratedcircuit fabrication processes. Resist, a photosensitive plastic, is spunon a workpiece, baked, and exposed in a pattern through a reticle,usually by ultraviolet (UV) light. After development and a second bake,the surface is left partially covered by an inert organic film thatresists various treatments to which the workpiece is subjected. Suchtreatments include material removal by wet chemical etch or by gaseousplasma etch, doping by ion implantation (e.g., broad beam implantation),and addition of material (e.g., lift-off). The preparation, exposure,development; clean, care, and stripping of resist can increase thenumber of fabrication steps tenfold, requiring expensive equipment andfacilities to establish stable, qualified, and high yield fabrication.

Photolithography has been the main lithographic tool for processingpatterns of resist down to 45 nanometers (run). However, present andfuture microelectronics will require minimum feature sizes below 45 nm.While advances in a number of lithography techniques (e.g., ultraviolet(UV), enhanced ultraviolet (EUV) emersion, maskless emersion, laser,phase-shift, projection ion, and electron beam lithography (EBL)) mayenable highscale production at these dimensions, they are all nearingtheir theoretical limits with respect to wavelength, overlay accuracy,and/or cost. Pushed to the limit, the weaknesses of each process presentdifficult problems, and the resulting patterning defects can result insignificant yield loss.

SUMMARY

In certain embodiments, a charged particle buncher includes a series ofspaced apart electrodes arranged to generate a shaped electric field.The series includes a first electrode, a last electrode and one or moreintermediate electrodes. The charged particle buncher includes awaveform device attached to the electrodes and configured to apply aperiodic potential waveform to each electrode independently in a mannerso as to form a quasi-electrostatic time varying potential gradientbetween adjacent electrodes and to cause spatial distribution of chargedparticles that form a plurality of nodes and antinodes. The nodes have acharged particle density and the antinodes have substantially no chargedparticle density, and the nodes and the antinodes are formed from acharged particle beam with an energy greater than 500 keV.

In certain embodiments, a charged particle buncher includes a series ofspaced apart electrodes arranged to generate a shaped electric field.The series includes a first electrode, a last electrode and one or moreintermediate electrodes. The charged particle buncher includes a bunchercontrol device configured to generate the shaped electric field whichcauses spatial alignment of charged particles such that the mass ofcharged particles is filtered by positional displacement forming aplurality of nodes and anti nodes along the axis I of propagation. Thenodes have a charged particle density and the antinodes havesubstantially no charged particle density, and the nodes and theantinodes are formed from a charged particle beam with an energy greaterthan 500 keV.

In certain embodiments, a charged particle funnel includes a series ofspaced apart electrodes arranged to generate a radial shaped electricfield. The series includes a first electrode, a last electrode and oneor more intermediate electrodes. The charged particle funnel includes abuncher control device configured to generate the radial shaped electricfield which causes the position of charged particles to be displacedradially to the direction of propagation while creating an axial timevarying electric field that causes a steady or segmented uniform spatialdistribution of charged particles that form a plurality of nodes andantinodes. The nodes have a charged particle density and the antinodeshave substantially no charged particle density, and the nodes and theantinodes are formed from a charged particle beam with an energy greaterthan 500 keV.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects, and advantages of the inventiondisclosed herein are described below with reference to the drawings ofpreferred embodiments, which are intended to illustrate and not to limitthe invention.

FIG. 1A is a perspective view of a prior art apparatus for controlledparticle beam manufacturing;

FIG. 1B is a top schematic view of the apparatus of FIG. 1A;

FIG. 2 is a schematic block diagram of a prior art charged particleexposure chamber;

FIG. 3A is a schematic block view of a prior art charged particlecolumn;

FIG. 3B schematically illustrates bunching of charged particles;

FIG. 3C schematically illustrates a prior art beam buncher;

FIG. 3D schematically illustrates a prior art beam blanker;

FIG. 4A illustrates an example writing strategy over a period of time;

FIG. 4B is a schematic block diagram of an example workpiece stage andcontrol electronics;

FIGS. 4C and 4D is a schematic block diagram illustrating an examplebeam measurement technique;

FIG. 5 illustrates example groups of charged particles in a digitalbeam;

FIG. 6A depicts a top schematic view of a deflector;

FIG. 6B is a perspective quarter cut-away view of the upper rightquadrant of the deflector of FIG. 6A;

FIG. 7 is a schematic block diagram of another example charge particlecolumn.

FIG. 8 illustrates an example writing strategy.

FIG. 9 is a perspective view of an example of a spatial charged particlebuncher according to certain embodiments described herein;

FIG. 10 schematically illustrates a quasi-electrostatic simulationshowing the formation of a steady stream of bunched charged particlesfrom a continuous charged particle beam with a well defined node andanti-node period;

FIG. 11 is a quasi-electrostatic simulation of the electric fielddistribution through a section of an embodiment of a spatial chargedparticle buncher;

FIG. 12A is a quasi-electrostatic simulation result of the periodic timevarying linear piecewise continuous triangular voltage waveform appliedto each electrode;

FIG. 12B is a quasi-electrostatic simulation result of the periodicstepped axial electric field in the excitation gap between two adjacentring electrodes;

FIG. 13 is a quasi-electrostatic simulation result of the periodic axialvariable amplitude electric field pulse train produced in the excitationgap between two adjacent electrodes formed by applying a periodic trainof variable amplitude voltage pulses to each electrode with the voltagesignals delayed between two adjacent electrodes by a delay equal to thecharged particle transit time through the region defined between twoadjacent electrodes;

FIG. 14 is a quasi-electrostatic simulation result of the periodicstepped axial electric field synchronized with the charged particle beamtravel so that every charged particle experiences a constant phase ofthe periodic stepped axial electric field as it propagates down the axisof the device from excitation gap-to-excitation gap;

FIG. 15 is an example of an embodiment of a voltage ladder circuit ornetwork that could be connected to each electrode to drive the operationof the spatial buncher; and

FIG. 16 illustrates different embodiments of the aperture shapes forelectrodes including straight wall, taper and bow tie.

DETAILED DESCRIPTION

Although certain preferred embodiments and examples are disclosed below,it will be understood by those in the art that the invention extendsbeyond the specifically disclosed embodiments and/or uses of theinvention and obvious modifications and equivalents thereof. Thus, it isintended that the scope of the invention herein disclosed should not belimited by the particular disclosed embodiments described below.

Embodiments of charged particle beam bunchers are described herein.Optional prior art environments of use for embodiments of methods foroperating charged particle beam bunchers are also described below and inU.S. Pat. No. 7,259,373, Which is incorporated herein by reference inits entirety.

Smaller device geometries may be achieved by direct writing with a beamof charged particles. Focused ion beam (FIB) systems generally do nothave sufficient ion exposure to support high throughput manufacturing.Furthermore, only relatively low speed deflection is available usingexisting ion optics/deflection electronics methodologies, preventingefficient direct write of layers patterned for semiconductor devices. Assuch, FIB has been limited to mask (e.g., reticle) and semiconductorrepair. As FIB technology progressed, it supported the ability tosimultaneously deposit, etch, and implant patterns directly onworkpieces without the use of resist. Problems remained, however,including low energy systems with little-to-no wafer writing software,no metrology systems, and minimal beam current densities and deflectionspeeds necessary to support the lithography on a high manufacturingscale. Modifications and improvements to FIB systems in accordance withembodiments described herein can achieve suitable manufacturingthroughput in both resist processing and resistless fabrication ofsemiconductor workpieces and other media (e.g., photomask, compact disk(CD), digital video disk (DVD), high definition DVD (HD DVD), Blue-Ray,etc.).

The physical properties of a beam of charged particles traveling alongan axis with a distribution transverse to the axis can be modified toprovide a high speed, digital (or “pulsed”) distributed writing beam.Various methods can be used to create a wave of temporally and spatiallydefined high-density charged particle nodes and low density (or nodensity) anti-nodes, traveling in a longitudinal path of acceleratedparticles (herein referred to as a “digitized beam”). For example, abeam buncher can be used to create localized groups (or “flashes” or“packets”) of the charged particles. These groups of charged particlesmay contain one or more charged particles. The digital beam is thenpassed through a deflector, whereupon variations in voltage cause thegroups of charged particles to change position relative to the directionof propagation. Changes in voltage can be timed in phase with theparticle nodes, thereby yielding efficient deflection. The presence of asharp edge of the antinode effectively provides. fast beam blanking fordirect write. Applying the digitized beam to the surface of a workpieceallows resistless patterned processing, including deposition, etching,and/or implantation of material to the surface of the workpiece and/orhigh resolution resist exposure.

FIG. 1A is a perspective view of an example apparatus 100. FIG. 1B is atop schematic view of the apparatus 100 of FIG. 1A. The apparatus 100comprises an exposure chamber 102, a load Jock chamber I 04, a transportmodule I 06, and a plurality of processing chambers I 08. Although notillustrated, it will be understood that the apparatus 100 comprises agas manifold system and an automated process controller, described inmore detail below.

The load lock chamber 104 may house workpieces 101 that are not beingprocessed, for example, before and/or after processing in the apparatus100. In certain embodiments, the load lock chamber 104 is configured toachieve vacuum such that an automated material handling system (AMHS)110 of the transport module 106 in communication with the load lockchamber 104 may insert and/or remove workpieces 101 without having to bepumped down to or up from vacuum between each transfer. In certainembodiments, the load lock chamber 104 is configured to accept a frontopening unified pod (FOUP).

The transport module 106 is configured to move workpieces 101 within theapparatus 100. The transport module 106 comprises an AMHS 110 configuredto manipulate at least one workpiece 101. A suitable AMHS 110 can bechosen based on the design of the exposure chamber 102, the load lockchamber 104, the transport module 106, and/or the process chambers 108.In certain embodiments, the AMHS 110 comprises a plurality of transportarms such that workpieces 101 may be manipulated simultaneously (or inparallel).

The transport module 106 can include a workpiece prealigner, such thatthe workpieces 101 removed by the transport arm 110 and subsequentlyplaced into the exposure chamber 102 or a process chamber 108 are in anorientation that is ready for processing in the exposure chamber 102 ora process chamber 108. For example, the prealigner may usecharge-coupled device (CCD) or other imaging devices to locate a flat,notch, or other identifying feature of the workpiece 101. The prealignercan be configured to determine overlay parameters of alignment featureson the workpiece 101. The overlay parameters may comprise x and yoffset, rotation, etc.

Depending on the type and size of the workpiece 101, a variety of vacuumand handling systems can be used in the apparatus 100. A system capableof processing a variety of workpieces preferably uses a high speedworkpiece. handling system. Workpiece into vacuum throughput can beincreased by aligning the workpiece under vacuum on the workpiece stageinstead of outside the vacuum system. A standard workpiece holder (e.g.,a wafer magazine) can be pumped to high vacuum within a few minutes.Alignment of the workpiece 101 under vacuum may increase wafer intovacuum throughput.

The transport module 106 can comprise one or more processingsubstations, for example comprise one or more buffer zones to holdworkpieces 101 between processing steps, a particle contaminationdetector, a temperature quenching station, and/or a metrology station.The metrology station may be selected from any tool appropriate for thattype of workpiece, including, but not limited to, an energy dispersiveanalyzer (EDS), a wavelength dispersive analyze (WDS), a secondary ionmass spectrometer (SIMS), a scanning electron microscope (SEM), atwo-dimensional laser scanning imager, a three˜dimensional imaging laserradar (LADAR), a thermal imager, a millimeter wave imager, a workpieceimager, and a camera.

The exposure chamber 102 is configured to expose a workpiece 101 to adigital beam of charged particles. As shown. in FIG. 2, the exposurechamber 102 comprises a beam column 200, illustrated in more detail inFIG. 3A. The beam column 200 comprises a charged particle source 202 forgenerating a stream of charged particles. Although systems and methodsare described in certain embodiments herein with reference to ions, itwill be understood that some systems and methods may utilize chargedparticles comprising electrons and positrons. Charged particles mayinclude one or more species of positively and negatively charged ions,as well as singly, doubly, triply, etc. charged ions. In someembodiments, the charged particle source 202 is adapted to generate aplurality of ion species. In some embodiments, the charged particlesource 202 is adapted to provide a current of 1,000 amperes/cm² (A/cm²)focused to a 10 nm spot as measured at the target.

Liquid metal ion source (LMIS) technology enables the formation of highcurrent density charged particle beams. An example technique to create aLMIS is a heated reservoir of liquid metal from which a needle protrudesdownward. The metal flows down the needle by capillary action. Anelectric field from an extraction electrode pulls the liquid at the tipof the needle into a sharp cusp (a “Taylor Cone”) from which ions areemitted. The point source is very bright (e.g., about 10⁹A/teradian/cm²), and, with suitable optics, permits the beam diameter tobe as small as 2 nm. A variety of alloys provides several ion speciescommon for semiconductor fabrication.

Accelerating and focusing a distributed energy of ions can introducechromatic aberrations resulting in a loss of current density efficiencyof the ion optic system. The ion beam energy distribution can bemeasured as the beam full-width-half-max (FWHM) and can be distributedas much as 12%. Improving the current density efficiency and resolvinglong and short term stability issues can make LMJS performance adequatefor a semiconductor processing tool. One aspect of various embodimentsof the present invention is the realization that beams of chargedparticles are composed of a distribution of high and low energy trails,which can be advantageously grouped.

At least two mechanisms can contribute to the broadening of the energydistributions: first, effects related to the formation of the ions; andsecond, space charge forces after ion formation. Ion emissions from aLMIS source are formed either by direct field desorption of an ion atthe emitter tip or by field ionization of desorbed atoms at somedistance from the emitter tip. Ions generated close to the tip surfacecan exchange charge with neutral atoms further downstream, forcing azero energy ion at that point. Since the electric field in the emitterarea is high (e.g., between about 20 and 50 Volts/nm), ions formed atdifferent distances from the emitter can have different energies. Spacecharge effects broaden the energy distribution of the beam, particularlyat low velocities. Therefore, the column 200 preferably is configured toaccelerate the ions to full energy directly after formation. The use oflow-mass species may aid in ion acceleration when the use of suchspecies is appropriate.

Space charge effects are also aggravated by higher currents. For theLMIS source, the width of the energy distribution is preferablyproportional to the current to the ⅔ power. As such, practicalapplication of traditional LMIS sources to lithography show behaviorsimilar to electron beams:

A limitation on the maximum current density achievable with LMIS-basedsystems results from the energy distribution of the ion beam that iscaused by the achromatic aberration in the upper ion optical system.However, the use of a beam digitizer 206 downstream of the chargedparticle source 202 that is configured to adjust the longitudinalspacing between charged particles so as to create temporally andspatially resolved groups of the charged particles along the axis ofpropagation can effectively slow faster moving particles and can speedslower moving particles to obtain a uniform velocity, and thus a uniformenergy distribution (accelerating voltage) within each group of thedigital beam, thereby reducing the effect of the charged particle sourcechromatic aberration, as illustrated in FIG. 3B.

Similar to the drift of an electron beam, a LMIS Taylor cone emissionunpredictably drifts in a FIG. 8 pattern over about a one hour period.Undetected, this drift can cause pattern placement errors. Sourcelifetime and current stability are barriers to the practical applicationfor production throughput processing tools using traditional LMISsources. Further improvements at the charged particle source 202 canimprove the stability and lifetime, thereby reducing frequent sourcereplacement. The broadening of the energy distribution associated withion formation can be reduced or minimized by operating the LMIS at lowtemperature, thereby decreasing the neutral atom density in theproximity of the tip. The energy distribution can also be reduced orminimized by choosing a low vapor pressure species, for example byselecting a doubly ionized species that has a low charge exchangecross-section and that is formed at the surface of the tip, known tohave a narrow energy distribution, and by using a species that has theadditional benefit of a small virtual source. It will be appreciatedthat other techniques can also be used.

Extended lifetime of the charged particle source 202 may be achieved byconditioning the source driving parameters prior to operation. As such,the incorporation of an automated conditioning routine can contribute tothe extended life and stability of the charged particle source 202.Additionally, a continuous flow strategy, such as impregnatedelectrode-type needles with hardened tips, can further extend the lifespan of the charged particle source 202. Second order effects ofimproved life span can include emission current and position stabilityimprovement. Source emission position stability can be successfullycorrected by using an error feedback from occasional beam registrationsand adjustment to. source servomotors. Although increased ion beamcurrent density is preferred, the column 200 in the exposure chamber 102need not increase the beam current density.

Other charged particle sources 202 may also be used with the embodimentsdisclosed herein. For example and without limitation, the chargedparticle source 202 may comprise a plasma ion source (PIS), a volumeplasma ion source (VPJS), a gas field ionization source (GFIS), a carbonnanotube field emitter, a free electron laser and a target, a pulsedlaser ablation ion source, a magnetically confined plasma anode source(MAP), and a thermal field emission (TFE) electron source.

The stream of charged particles. emanating from the charged particlesource 202 is collimated and directed along an axis by a collimator 204.A variety of collimators 204 comprising a combination of opticalelements are appropriate for use in the column 200. For example, andwithout limitation, the collimator 204 may comprise two or more lensesor a lens and a reflective optic. The collimator 204 may furthercomprise an aperture configured to shape the charged particle beam. Thecollimator can be adapted to direct the charged particle stream ataccelerating potentials between about 5 and 30 kilo electron volts(keV). The exposure chamber 102 can be adapted to direct the chargedparticle stream at accelerating potentials between about 5 and 500 keV.A voltage of the collimator 204 can be additive to additional voltages,for example applied by a lower column exit aperture.

If the charged particle source 202 is adapted to generate a plurality ofion species, individual ion species can be selected for specificprocessing applications by filtering the charged particle stream with aparticle filter (e.g., a spectrometer filter). For example, a massseparator can be configured to deflect selected ion species into a massseparator aperture plate. The mass separator is preferably disposedbetween the collimator 204 and the beam digitizer 206. The massseparator can comprise a reflective optic, an ExB lens, and/or a Weinfilter.

The beam digitizer 206 is configured to create a digital beam comprisingdiscrete groups of at least one charged particle by adjusting thelongitudinal spacing between charged particles along the axis ofpropagation. For example, the beam digitizer 206 can be configured tocreate groups. comprising between about 1 and 7,000,000 chargedparticles, between about 1 and 100,000 charged particles, between about1 and 10,000 charged particles, or between about 1 and 50,000 chargedparticles. The beam digitizer 206 can be configured to createlongitudinal spacing D between groups of charged particles of less thanabout 10 m of beam travel, less than about 1 m of beam travel, less.than about 10 cm of beam travel, less than about I 0 mm of beam travel,less than about 1 mm of beam travel, less than about 500 μm of beamtravel, less than about 300 μm of beam travel, less than about 100 μm ofbeam travel, less than about 10 μm of beam travel, less than about 100nm of beam travel, less than about 10 nm of beam travel, or less thanabout 1 nm of beam travel between the groups of charged particles. Thebeam digitizer 206 can also be configured to create longitudinal spacingbetween the groups of charged particles of between about 1 nm and 10 mof beam travel, between about I run and 1 m of beam travel, betweenabout 1 nm and 10 cm of beam travel, between about 1 nm and 10 mm ofbeam travel, between about 1 nm and 1 mm of beam travel, between about Inm and 500 μm of beam travel, between about I nm and 300 μm of beamtravel, between about 1 run and 100 μm of beam travel, between about 1nm and 10 μm of beam travel, between about 1 nm and 100 nm of beamtravel or between about 1 nm and 10 nm of beam travel. The longitudinalspacing between the groups of charged particles may be substantiallyequal, unequal, periodic, harmonic, etc.

The beam digitizer 206 can comprise a beam buncher. In a radio frequency(RF) beam buncher, a stream of charged particles pass through a bunchergap where they are acted upon by an alternating potential, RF ormultiple modulating potential wave forms, beat wave, harmonic, variable,or a combination thereof. Velocity modulation compresses the chargedparticles together so that they form spatially and temporally resolveddiscrete groups of charged particles. The frequency and the buncher gaplength can be configured to match a mean velocity of the groups ofcharged particles. The applied potential modulates the longitudinalvelocity of each charged particle as they pass through the buncher gapso that some charged particles (e.g., charged particles with a lowervelocity than the mean velocity) are accelerated while other chargedparticles (e.g., charged particles with a higher velocity than the meanvelocity) are decelerated (e.g., as depicted in FIG. 3B). The gap lengthof the buncher gap, the magnitude and frequency of the appliedpotential, and the time of flight (TOF) of the charged particles throughthe column 200 determine the final characteristics of the digital beamand the groups of charged particles at the surface of the workpiece 101.

FIG. 3C schematically depicts a stream of charged particles travelingthrough a beam buncher. A potential can be applied across the electrodes302, 304 of the beam buncher that are separated by buncher gap G. Ifunaltered thereafter, the charged particles begin to form groups whoselength L and separation (spacing) D depend on how far the chargedparticles have traveled after passing through the beam buncher. The beambuncher can be configured to compress the charged particles into groupsduring travel or to apply an electric field to longitudinally compressthe groups of charged particles. The charged particles are preferablyfully compressed in the longitudinal direction when they reach theworkpiece 101 (e.g., as depicted in FIG. 3C). The energy applied by thebuncher can be determined by the difference between the initial energyof the stream of charged particles and the final energy of thetemporally and spatially resolved groups of the charged particles.

The beam buncher can comprise a plurality of buncher electrodes andtherefore a plurality of buncher gaps. The potential can be selectivelyapplied across two of the electrodes in order to change thecharacteristics of the digital beam. For example, a potential can beapplied across electrodes with a buncher gap G of 1 μm to create nodeswith a lower charged particle density and applied across electrodes witha buncher gap G of 3 cm to create nodes with a higher charged particledensity.

The relationships between beam buncher input parameters such as beamenergy and buncher current, frequency, and gap length and beam buncheroutput characteristics such as separation D, length L, and density arewell known. The beam buncher is preferably operated to provide a givennumber of charged particles per group. First, the buncher gap,frequency, and beam energy can be held constant while the current isadjusted. Second, the beam energy and buncher current can be heldconstant while the buncher gap and frequency are adjusted. Otheroperation configurations are also possible.

The beam buncher can comprise a helical coil that is modulated with acurrent frequency, resulting in a magnetic field. The longitudinalspacing (“gap”) between turns of the coil, the magnitude and frequencyof the applied current, and the time of flight (TOF) of the chargedparticles through the column 200 determine the final characteristics ofthe digital beam at the surface of the workpiece 101. For example, thefrequency and longitudinal spacing between turns of the coil can beconfigured to match a mean velocity of the digital beam.

Bunching charged particles allows write strategy optimization with dosevariations at the charged particle level by varying the beam buncherfrequency, amplitude, I and duty cycle, which in tum varies the chargedparticle density, as described above. The beam buncher parameters aretherefore preferably adjusted according to the write strategy.

The beam digitizer 206 can comprise a beam blanker (e.g., a beam blankerthat can operate at speeds sufficient to create a digital beam). Forexample and without limitation, the high speed blanker may comprise anaperture plate-configured to absorb the charged particle beam at certaininterval. The aperture plate is initially positioned such that thestream flows through the aperture in the aperture plate proximate to aninterior edge of the aperture plate. An electrode is configured todeflect the stream into the aperture plate, which intercepts the flow ofparticles to create a temporally and spatially resolved digital beam. Anaperture plate 316 is positioned proximate to the stream of chargedparticles. The electrodes 312, 314 are configured to apply a potentialto the charged particle stream to create temporally and spatiallyresolved groups of charged particles of the digital beam. If unalteredthereafter, the charged particles continue to travel with length l andseparation D regardless of how far the charged particles have traveledafter passing through the high speed blanker.

Other embodiments of the beam digitizer 206 are also possible. In someembodiments, the beam digitizer 206 is configured to modulate an on/offstate of the charged particle source 202. In some embodiments, the beamdigitizer 206 is configured to modulate a position of the chargedparticle source 202 longitudinal to the axis so as to displace thegroups of charged particles.

The beam digitizer 206 can be configured to apply electromagneticradiation, for example with a frequency of between about 1 megahertz(MHz) and 100 gigahertz (GHz) or between about 1 MHz and 25 GHz. Thebeam digitizer 206 can be configured to modulate, for example, theamplitude of the electromagnetic radiation, the frequency of theelectromagnetic radiation, combinations thereof, and the like. The beamdigitizer 206 can also be configured to apply a beat wave to a plasmacomprising the charged particles, to apply space charges to wake fields,to resonantly absorb the space charges, to blank the beam through anabsorption aperture, to apply a pulsed incident neutralizing beam to thecharged particle source 202, and/or to apply a pulsed laser beam to thecharged particle source 202.

Components described herein can be advantageously combined. The column200 can comprise a beam blanker downstream of the collimator 204 and abeam buncher downstream of the beam blanker. A digital beam coming fromthe beam blanker and into the beam buncher can be used to furthertemporally and spatially resolve the individual groups in the digitalbeam. The column 200 could comprise a beam buncher downstream of thecollimator 204 and a beam blanker downstream of the beam buncher. Otherconfigurations are also possible.

The column 200 further comprises a deflector 210 downstream of the beamdigitizer 206. The deflector 210 comprises a series of deflection stages(e.g., electrode stages, magnetic stages) disposed longitudinally alongthe axis of the digital beam. The deflector 210 deflects individualgroups of charged particles in the digital beam. As used herein, thephrase “minor field deflection” refers to the deflection of anindividual group of charged particles by the deflector 210. Thedeflector 210 can be configured to deflect the groups in the digitalbeam substantially perpendicularly to the axis of propagation. Forexample, the deflector can comprise between about 1 and 1,000 or fourdeflection stages or at least one, two, three, or four deflectionstages. Each deflection stage can comprise two or more electrodes orfour electrodes. Other quantities of deflection stages and electrodesare also possible.

An average or mean velocity of the groups of charged particles in adigital beam can be between about 1×10⁴ meters/second (mis) and 3×10⁸m/s. Application of potentials by each of the deflection electrodestages can be adapted to be synchronized with the mean velocity of thegroups of charged particles passing through the deflector. For example,a deflection electrode stage may be adapted to apply a voltage only whena group of charged particles is passing through the deflector in generaland through that particular deflection electrode stage in particular.Application potentials by each of the deflection electrode stages can beadapted to be harmonically synchronized with a mean velocity of thegroups of charged. particles passing through the deflector. For example,each deflection electrode stage in at least a portion of the deflectormay be adapted to apply a voltage only when a particular group ofcharged particles is passing through the deflector in general andthrough that particular deflection electrode stage in particular.Application of potentials by each of the deflection electrode stages canbe adapted to be randomly synchronized with a mean velocity of thegroups of charged particles passing through the deflector. As usedherein, the phrase randomly synchronized is to be given its broadestpossible meaning including, but not limited to, synchronization ofapplication of voltage by the deflection electrode stages to groups ofcharged particles with random spacing or synchronization of applicationof voltage by random deflection electrode stages to groups of chargedparticles with random or other spacing.

Electrodes of the deflection stage can apply a substantially equalvoltage potential as each group of charged particles of the digital beampasses. The amount of deflection of each group of charged particlesdepends on the number of electrodes activated sequentially. Variablepotentials can be applied to each deflection electrode stage as eachgroup of charged particles passes. For example, the first deflectionelectrode stage has the smallest voltage with subsequent electrodes haveprogressively more voltage, resulting in a linear deflection aselectrodes are activated. The converse is also possible, where the firstdeflection electrode stage has the largest voltage with subsequentelectrodes having progressively less voltage. The number of deflectionelectrode stages activated defines the amount of deflection of eachgroup of charged particles of the digital beam. The signal timing andnominal voltages applied to the deflector can be calibrated forindividual deflection electrode stages and even individual electrodeswithin each deflection electrode stage. Triggering an applied voltage ofindividual deflection electrode stages can be delayed if needed to matchthe incidence of to each group of charged particles of the digital beam(“phase-matching”), for example due to changes in charged particlevelocity, species, and mass, deflection stage position, patternresolution, pattern field errors, errors within an objective deflectionfield, process specific compensation and write strategies, combinationsthereof, and the like. A field perimeter of the deflection electrodestages can be defined as the minor deflection field of less then 4 mm,less than 2 mm, less than 1 mm, or less than 100 μm displacement in x ory from the center of the axis of propagation.

The potentials of each of the deflection electrode stages can be adaptedto partially displace the groups of charged particles towards anintended trajectory. Each group is partially deflected I/Nth of anintended deflection distance by each of a number N of deflectionelectrode stages. The first deflection electrode stage, or any singledeflection electrode stage, can be adapted to substantially fullydisplace one or more (e.g., all) groups of charged particles towards anintended trajectory, and the other deflection electrode stages are usedto fine tune the deflection of the groups. Other combinations are alsopossible.

For example, the harmonically synchronized deflector described above, atleast a portion of the deflector can comprise N sets of deflectionelectrode stages, each set of deflection electrode stage comprising Ndeflection electrodes, in which every Nth deflection electrode stage isconfigured to displace a particular group of charged particles towardsan intended trajectory. If at least a portion of the deflector comprisestwo sets of deflection electrode stages, every other deflectionelectrode stage in the sets of deflection electrode stages may beconfigured to displace a particular group of charged particles towardsan intended trajectory. If at least a portion of the deflector comprisesthree sets of deflection electrode stages, every third deflectionelectrode stage in the sets of deflection electrode stages ma) beconfigured to displace a particular group of charged particles towardsan intended trajectory. Other variations and configurations arepossible.

FIG. 6A depicts a top schematic view of a deflector 210 comprising atleast one electrode in each deflection electrode stage. The digital beamcomprising charged panicles is configured to flow through the centeraperture of the deflector 602. The sets of electrodes 604, 606 and 608,610 may be positively or negatively charged such groups of chargedparticles are deflected perpendicularly to the longitudinal axis of thedeflector and the path. Preferably, the electrodes on opposing sides,for instance, electrodes 604 and 606, are oppositely charged. FIG. 6B isa perspective quarter cut-away view of the upper right quadrant of thedeflector 210. The electrodes 606 are separated in this embodiment by aninsulator 612. Examples of insulator materials include SiO₂, SiN_(x),SiO_(x)N_(y), combinations thereof, and the like. It will be understoodthat rather than a single deflector comprising a plurality of deflectionelectrode stages, the deflector 210 may comprise a series of deflectors,each comprising one or more deflection electrode stages. For example, adeflector 210 may comprise three sets of deflectors. As illustrated inFIG. 6B, the groups of charged particles are deflected by eachdeflection electrode stage as they travel along the path. Otherdeflector and electrode configurations are possible.

In certain embodiments, the deflector 210 is configured to arrange thegroups of charged particles into a three-dimensional time space (an“adaptable virtual digital stencil”). In certain embodiments, thedeflector 210 is adapted to create a laterally distributed pattern ofthe groups of charged particles. In some embodiments, the deflector 210further comprises a deflector lens adapted to demagnify the pattern orthe virtual stencil. The deflector lens can comprise an electrostaticlens, an electromagnetic lens, a reflective lens, a combinationreflective and refractive lens, a combination reflective and deflectivelens, a combination deflective and refractive lens, combinations of thesame, and the like. FIG. 7 is a schematic block diagram of a column 200in which the groups of charged particles coming out of the deflector 210are arranged in a visual digital stencil 702, each group of chargedparticles having undergone a minor field deflection. The objective lensassembly 212 is configured to deflect the virtual stencil with a majorfield deflection. The combination of minor field deflection, major fielddeflection, and movement of the workpiece 101 can be used to expose apattern of charged particles on the workpiece 101.

In certain embodiments, a phase of the groups of charged particles ofthe digital beam longitudinal to the axis is configured to besubstantially equal, single harmonic, multiple harmonic random,combinations thereof, and the like. The spacing between the deflectionstages may be adapted to be synchronized and to be in phase with thegroups of charged particles. In some embodiments, longitudinal positionsof the deflection electrode stages are adjustable. In some embodiments,the deflector 210 comprises a digital feedback system, for example toadjust the spacing between the deflection electrode stages. Piezos, etc.may be used to position the electrodes or deflection stages.

In some embodiments, the column 200 further comprises an objective lensassembly 212 disposed between the deflector 210 and the workpiece stage214. The objective 212 may comprise a lens, a mirror, a reflectiveoptic, a combination reflective optic and refractive lens, a combinationreflective optic and deflection electrodes, a combination deflectionelectrode and refractive lens, combinations of the same, and the like.In some embodiments, the objective lens assembly 212 comprises adetractive lens assembly or a deflector electrode assembly configured todemagnify, focus, and/or deflect the groups of charged particles or theadaptable virtual digital stencil. For example, in certain embodimentsand without limitation, groups of charged particles having a diameter(or “spot size”) of about 200 nm are reduced I 0 times to a diameter ofabout 20 nm. The objective lens assembly 212 may also be adapted todemagnify the groups or the stencil by 100 times or 1,000 times. Inembodiments in which the objective lens assembly 212 is configured todeflect a virtual digital stencil, the deflection may be called a “majorfield” deflection. In some embodiments, a field perimeter of theobjective lens assembly 212 is defined as the major deflection field ofless then 10 mm, less than 5 mm: less than 1 mm, or less than 100 μmdisplacement in x or y from the center of the axis of propagation. Incertain embodiments, the exit aperture comprises an exit aperture.

Referring again to FIG. 2, the exposure chamber 102 comprises aworkpiece stage 214 downstream of the lower objective lens assembly 212.The workpiece stage 214 is configured to hold the workpiece 101.Preferably, the workpiece stage 214 comprises an interferometric stage,wherein the relative position of the stage is measured using opticalinterference. The workpiece stage 214 may be thermally controlled toreduce magnification errors in the workpiece, which can lead to overlayerrors. The workpiece stage is preferably configured to continuouslymove while a workpiece 101 is exposed to the groups of chargedparticles. For example, the workpiece stage 214 may be configured tomove continuously over a dimension of 25 centimeters over a period of 1second during exposing. For another example, the workpiece stage may beconfigured to move without stopping for more than 5 nanoseconds per 0.5seconds during exposing. The ability to continuously expose while movingthe workpiece stage 214 without stopping can yield increase efficiencyand throughput.

In certain embodiments, the workpiece stage 214 comprises aninterferometer configured to determine the location of the workpiecestage 214 in a horizontal plane. The relative x/y position of the stagecan be measured using optical interference. Other methods are alsopossible, for example the workpiece stage may comprise a registrationmark, grid, or feature detectable by a secondary ion mass spectrometer(SIMS), backscattered electronics, or faraday cup disposed below theregistration grid. The registration. mark is preferably included in anassembly that can be moved parallel to the column 200 in order tooptimize a working height of the registration mark to the workpiece,thereby reducing column calibration and registration errors. The digitalbeam may periodically or randomly be directed towards the registrationmark to check the alignment of the column. The registration mark mayalso be used to calibrate the column 200 before, after, and/or duringexposing a workpiece.

In some embodiments, the chamber 102 further comprises a height controlsystem that measures the height of the workpiece stage 214 and/or aregistration mark. The height control system can include, for example, alaser and a plurality of detectors configured to receive light emittedfrom the laser and reflected by the workpiece, the workpiece stage 214,and/or a surface that moves with the workpiece. The height controlsystem can compensate for variation in the measured height of theworkpiece stage by adjusting an elevation of the stage, for example byusing electrostatic clamps, piezoelectric devices, etc. In someembodiments, the height control system is configured to compensate forheight variations of less than J μm. Electrostatic clamping may be usedto secure the workpiece to the workpiece stage 214 and to ensureadequate thermal contact and flatness of the workpiece.

Full motion writing (FMW) can eliminate the workpiece stage motionoverhead time while exposing a workpiece. In FMW, the deflector 210system is updated in real time to track the motion of the workpiecestage 214, thereby allowing the system to write patterns while theworkpiece stage is in motion. Such a process preferably uses a highspeed optical controller (e.g., laser) to track the position of theworkpiece stage 214. For example, circuitry on the controller canconvert Doppler-shifted laser deflection measurement& into laser pulsesthat can be stored in a stage position register. Interferometry, laserdeflection measurements, or other optical techniques can be used totrack the position of the workpiece. Therefore, the throughput oflithography systems can be improved by reducing or eliminatingnonexposure time during stage repositioning and settling sequences.

While exposing a workpiece, each deflection field center is defined by awindow of opportunity (WOO). While the workpiece stage is in motion anda reflection field passes over an unwritten WOO, a stage controllersignals a deflection controller to initiate exposure. The workpiece isexposed while the undeflected beam center passes through the WOO. Withinthe WOO, the deflection system can deflect to the outer limit of thefield. During this time, the deflection system is updated by theworkpiece stage position register of the actual location of theworkpiece stage.

The workpiece stage can allow real time deflection correction. Bychanging the WOO size or frame size, or by smoothing the frame-by framepattern data, the system can be dynamically optimized for continuouswriting. A typical frame/WOO density is depicted in FIG. 4A.

The workpiece stage may be configured to provide suitable velocityperformance, for example at 100 centimeters per second. The workpiecestage may be configured to rotate a workpiece during exposure at up toabout 40,000 rotations per minute (rpm). For example, the workpiecestage may have as little inertia as possible, and a compatible workpiecestage motor design can be provided. The use of vacuum compatible airbearing rails and linear motor drives can provide adequate decoupling ofvibration sources. As additional examples, the workpiece stage motorscan be placed in the vacuum system, light weight materials can be usedfor the workpiece stage, and the workpiece can be aligned on the stage,thereby eliminating the workpiece cassette and cassette clampinghardware. Additionally, the first three derivatives of stage position(velocity, acceleration, and jerk) can be limited and damped byelectronic hardware to properly control the motion of the workpiecestage. FIG. 4B is a schematic diagram of an example workpiece stage andcontrol electronics.

The exposure chamber 102 may be in communication with controlelectronics, for example system support electronics 220 including waferhandler control, vacuum control, suspension control, temperaturecontrol, pressure control, etc. and column support electronics 230including a source control module, digitizer control, deflector control,lens control, wafer height sensor, video processor, stage control, and adynamic corrector (e.g., for real time column aberration correction).The column support electronics 230 may be in communication with dataprocess electronics 240, for example a workstation.

An example application of the systems described herein is to perform insitu workpiece processing or resist exposure by directly writing on theworkpiece. Preferably, accurate registration of optics to the targetworkpiece is achieved, but tool induced shift (TIS) and workpieceinduced shift (WIS) errors may be introduced due to temperature effects,workpiece processing effects, and optical distortions. An examplesolution is to measure an initial pattern (e.g., one or more alignmentmarks) on the workpiece is and to use the measurement data to accuratelyplace a newly patterned image onto the workpiece, for example byadjusting the exposure parameters.

A registration sensor preferably can automatically detect and recognizea variety of registration and alignment mark patterns, materials, andprofiles without impacting the quality of exposure throughput. Examplesto achieve such a sensor include, but are not limited to, using a highresolution, high speed registration system with existing hardware,determine the limitation and flexibility of the registration strategy(e.g., by mapping the workpiece with die-to-die registration) and theincorporating a temperature conditioning stage, and introducing a highspeed moire (grating) interferometer system for die-to-die registration,combinations thereof, and the like. Other approaches are also possible.

A high resolution, high speed registration system can employ existinghardware and can be similar to existing electron beam registration, buta plurality of imaging modes can be used. Scanning the surface of anobject (e.g., a registration or alignment mark) with a digital beamproduces secondary electron emission, secondary ion emission, and ionsputtering. A bi-axial or cylindrical microchannel plate can be used todetect both secondary electrons (e.g., by biasing above the voltage ofthe target) and the secondary ions (e.g., by biasing below the voltageof the target). Other configurations are also possible. An image can becreated by measuring a signal yield of the secondary ions and secondaryelectrons at each point where the beam impacts the target. Variations inthe yield indicate changes in surface topology or composition of theworkpiece. The position resolution of this signal is a product of themeasured beam spot size and deflection pixel size during registrationand is augmented by statistical metrology. Sputtered ions providegreater mark recognition ability I because such ions can be collectedand mass analyzed secondary ion mass spectroscopy (SIMS). SIMSregistration techniques are well developed and can be used both for markdetection and for process development diagnostics. An atomic map withthe spatial resolution of the beam spot size can provide excellentprecision for mark detection.

To optimize registration, a product summation of the detector videosignal with a computer generated image of the registration or alignment.mark can be used to enhance or recover an otherwise unrecognizabletarget signal from high-noise background. This can be performed byautomatically correlating the video gain and bias offset for an initialsignal enhancement. Once the tone is properly adjusted, the signal canbe correlated with a computer generated (CAD) image of the registrationor alignment mark to provide an enhanced image of the mark. Othersignals are detectable from digital beam mark interaction. Signals suchas those from secondary electrons and backscatter electrons may be usedfor this process. Additionally, signals from secondary electrons andbackscatter electrons may be employed differentially to improvedetection limits (e.g., signal to noise ratios). For example, the finaldetection signal may be the difference between SIMS and other signals.The speed of registration may be limited by the quality of theregistration electronics, but incorporating modem electronics (e.g.,digital signal processing (DSP)) may reduce the registration time byorders of magnitude without burdening registration resolution.

Another consideration in the quality and speed of registration is theconfiguration used to register to the workpiece prior to exposing.Depending on the preconditioned and. in-process temperature stability ofthe workpiece, several strategies are available to compensate fordistortions and throughput issues. Workpiece mapping generally registersa single die, providing reduced or minimum overhead to the systemthroughput but no correction for pattern distortion caused bytemperature instability during exposing. Die-to-die registrationperformed immediately prior to die exposure, for example to minimizetemperature distortion effects, generally uses four registrations perdie per level. Such a technique eliminates the ability to write in aserpentine mode, drastically limiting the throughput of the system bymemory load overhead time. However, performing registration on aplurality of dies at one time can maintain the ability to write in aserpentine mode within a field comprising the plurality of dies, therebyallowing increased or maximum throughput while reducing or minimizingpattern distortion.

Overlay accuracy becomes increasingly important as device geometriesshrink. For a digital beam tool, the direct exposure of multilevelpatterns on a single workpiece for manufacturing of integrated circuitsdesirably. includes accurate intra-layer registration. An exampleworkpiece alignment technique has three features: adequate signalgeneration from the surface impact of the digital beam; a detectionalgorithm for processing the detected signal; and an alignment featurefabrication technique.

The, impact of a charged particle onto the workpiece can create mediasuch as secondary electrons, backscattered electrons, photons, andsecondary ions, each having certain advantages in detection efficiency.However, selection of a particular media for registration purposesdepends on the charged particle species, the charged particle energy,and the current density of the beam. A signal detector may be optimizedfor a given media. For example, an electron-photomultiplier is generallyappropriate for secondary electrons, a solid state diode is generallyappropriate for backscattered electrons, and secondary ion massdetectors are generally appropriate for photons and secondary ions.

A digital signal processor processes information from the signaldetector in order to determine the location of the alignment mark. Atraditional method of detection includes a one-dimensional line scanwith the digital beam. As the digital beam transitions by deflectionacross the alignment mark, the detected video signal. is modulated.Modulation occurs because differences in the alignment mark and thecontour of the workpiece. Actual alignment mark location can bedetermined by processing the distribution of the modulated signal via adigital signal processing module. Another detection method includes anX/Y scanning mode of the digital beam to acquire a video image of thealignment mark. To achieve accurate edge detection, digital signalprocessing algorithms are applied. Improved detection of the alignmentfeature edge is accomplished through a two-dimensional imaging methodthat averages several frames of video data and determines the actuallocation of the alignment mark by gray scale signal processing.

Preferably, alignment marks are formed over the entire working area ofthe workpiece in the form of equally spaced two-dimensional grids. Oneconstruction method is the formation of a raised multilayeredsemiconductor structure consisting of layers of silicon, silicon dioxide(SiO₂), and polysilicon, with an alignment mark formed on thepolysilicon layer of the wafer. In another construction method, analignment mark is etched into the surface of a silicon wafer and a layerof a heavy metal (e.g., tantalum or tungsten) is deposited into thetrench. The alignment mark containing the heavy metal exhibit a highlevel of backscatter relative to a silicon substrate, thereby providingcontour details for low energy backscatter ion detection. Selection ofan appropriate alignment feature construction method depends on thesignal media and the signal detector, dictated by process steps.

A minimum of three alignment marks are preferred in order to accuratelyidentify translation, rotation, and magnification errors. The measurederrors are fed back to the workpiece stage control system forcorrection, thereby reducing workpiece and tool induced shift errors.The processing of global alignment marks may permit faster and moreaccurate detection of localized alignment marks by removing grosserrors. The alignment process can be repeated whenever the workpiece isinserted into the exposure chamber, whenever the workpiece is removedfrom the apparatus, between significant process steps, etc. Othertechniques can also be used.

Patterning tools transfer large quantities of microelectronic circuitpattern data in a format that can be manipulated (e.g., converted fromdigital to analog) within small periods of time (e.g., nanoseconds). Thedata is typically in a format for very large scale integration (VLSI)computer aided design (CAD), as described below. This data is used, forexample, to control the deflection by the deflector 210, the deflectorlens, the objective lens 212, and/or movement of the workpiece stage 214and can be adjusted to address aberrations in the optics. Chargedparticle exposure chambers may have imperfections (e.g., aberration,deflection errors), for example due to manufacturing or installationimperfections and the physical constraints of the optics. As an example,if a system is installed with a slight rotation relative to theworkpiece stage 214, beam deflections will be rotated relative to themotion of the workpiece stage 214. More complex errors may also bepresent; for example, an attempt to trace the outline of a large squarewith the beam may produce a pincushion or barrel shaped pattern. Themagnitude of these effects is proportional to the magnitude ofdeflection of the digital beam, which can limit the size of thedeflection field and can create nonlinear distortions in system writingquality. High resolution writing using a digital beam is thereforepreferably able to augment transformed pattern data to compensate fordeflection field distortion, wafer distorted pattern placement errors,stage position, etc.

Additionally, processing errors may be introduced. Pattern distortion ordeflection distortion can result from several factors when exposing aworkpiece with a digital beam. For example, thermal fluctuations in theexposure chamber 102 or in a workpiece 101 can cause magnificationerrors. For another example, securely clamping the workpiece 101 to theworkpiece stage 214 can also cause rotational errors or can inducestresses resulting in pattern sheering. For yet another example,unrecoverable nonlinear pattern distortions can result from subsequentprocessing such as rapid thermal annealing. For still another example,manufacturing or installation of the optics may be imperfect (e.g., witha slight rotation relative to the workpiece stage) and the optics havecertain physical constraints. More complex errors may be introduced bycertain processes, for example and without limitation, tracing a largesquare with the digital beam may result in a pincushion or barrel shapedpattern. The magnitude of the errors may be proportional to themagnitude of the beam deflection such that they can limit the size ofthe deflection field and can create nonlinear distortions in systemwriting quality. The adaptable virtual digital stencil is in softcode atany given point in time. As such, the stencil is temporally andspatially adaptable to correct in real time for nonlinear patternoffset, gain, rotation, and corrections within the minor field, whilebeing deflected in the major field. These corrections can be performedwithin features, die, or to the entire workpiece.

Digital beam lithography systems preferably can perform pattern and beamcorrections to compensate for processing-induced errors on the workpieceand optical errors (e.g., coma distortion, astigmatism, image puredistortion, chromatic aberration, spherical aberration, field curvature,etc.). Such corrections can improve writing quality and enhance systemthroughput.

Pattern and deflection distortion problems can be corrected byincorporating data manipulation bias electronics (hardware and software)into the system. For example, process control software can use metrologymeasurements to correct the deflection of the digital beam. Suchmetrology measurements preferably are made prior to exposing theworkpiece. The quality of the digital beam may initially be optimized toprovide improved or optimum measurements from subsequent metrology. Insome embodiments (e.g., as depicted by FIG. 4C), a knife-edged micromeshgrid is placed over a diode detector, which is scanned by the digitalbeam. The second derivative of the beam current with respect to the scanposition provides a high resolution beam profile (e.g., as depicted byFIG. 4D). Optimization (e.g., automated optimization) of the beamprofile with the optics control system allows focusing of the beam.

Once the digital beam has been optimized at small or minimum deflectionangles, the system can correct the digital beam profile within a largerusable deflection field by moving the workpiece stage 214 to a pluralityof positions within the outer limits of the distorted deflection field.The digital beam is then deflected to the position where the grid isscanned for beam optimization. The sequence is repeated over an extendedsize of the deflection field. Beam optimization data can then becorrelated with an interferometer or other position monitoring system ofthe workpiece stage 214. In certain embodiments, the linear contributionof the error is stored as an argument, while the nonlinear error isstored as pure memory. Beam distortions that depend on the position of aminor field within a major field can also be correlated. Within theminor field, use of the grid to calibrate deflection distortions can beperformed without moving the workpiece stage by major field deflectionof the adaptable virtual digital stencil to fit the scans on the grid.As a result, automated optimization or improvement of the beam profilecan be performed within an extended deflection system, thereby allowingimproved writing quality and throughput performance.

A final measurement can be made prior to exposing portions (e.g.,individual dies) of the workpiece 101 because the workpiece 101 may berotated or distorted as a result of temperature or stress effects causedby processing. If a pattern is being written on a workpiece 101 thatalready contains previous pattern levels, the new level can be adjustedto overlay on the previous levels, for example by registering to threeor four comers of the die and then applying a magnification orrotational correction within each die. For example, the calibrationsoftware may automatically measure features on the edges of each dieprior lo exposure and use the measurements to correct for any patterndisplacement, magnification, or rotation caused while aligning,processing, or handling the workpiece.

As described above, the exposure chamber 102 can be operated byproviding integrated circuit (IC) design data, for example in the formof CAD schematics, to generate and expose the pattern on the workpiece.Users of the apparatus 100 input a desired pattern to be written, alongany specific alignment configurations and/or processing parameters. Oncethe design for a device (e.g., an integrated circuit) is developed,multiple pattern layers of the design can be laid out to cover theworkpiece as desired (e.g., to cover the entire workpiece). A completeexposure data preparation (EDP) package with a user interface can beused to convert raw designs (e.g., in CAD or graphic data system(GDSII)) to a format usable by the exposure chamber 102 (e.g., exposureready format (ERF)). Prior to loading pattern data onto the system,several format changes, such as compressing and merging similar patternfeatures and reducing overlapping routines, can be made to increase ormaximize throughput of the exposure chamber. Once the pattern data hasbeen compressed to a reduced or minimum size, a field partition routinecan define the major and minor deflection fields of the pattern data anduse a smoothing routine to normalize the density in each data frame.Normalization reduces stage jerking when writing repetitious adjacentmultiple density patterns. After registration as described above, thepattern is laid out on the workpiece, using the registration data tocalibrate the intended beam pattern to the actual workpiece pattern andto apply any compensation to improve overlay accuracy.

In various embodiments, for example pattern data in GDSII, OASIS, orother suitable formats is input into the system. The input data is thenfractured into subfields and identified as to whether they are to be“written” or “non-written.” The mapping of the written subfields is sentto a data path module for rasterization (e.g., conversion to a bitmap).Throughput improvement is achieved by moving the workpiece stage anddeflecting the beam from one written subfield to a non-adjacent writtensubfield without exposing non-written subfields. No time is spentprocessing non-written subfields without pattern data.

Various deflection technologies can be used to expose a workpiece tocharged particles. Raster scan is a scanning mode in which the beammoves back and forth over the entire workpiece; the beam is turned onover designated areas and is turned off until the next designated area.Vector scan is a scanning mode in which the digital beam scans onlyselected areas where pattern is to be placed; after scanning of theselected area is completed, the beam is turned off and moved to selectedarea to be scanned. Hybrid vector raster technology utilizes a vectorapproach for major field deflection between data pattern subfields anduses a raster scan technology to deflect a Gaussian or shaped digitalbeam within the subfield. Throughput improvement can result from onlymoving the workpiece stage to positions that receive exposure. Anotherform of vector-raster includes a vector deflection in the major field, avector deflection between pattern features within the minor field, and araster image of the feature within the minor field. The vectorcapability of a vector-raster system can provide higher throughputversus a pure raster scan system, and the raster capability of thevector-raster system permits good pattern fidelity and high current witha small dwell time.

As described above, in certain preferred embodiments, minor fielddeflection of the digital beam is accomplished through a deflector,which is possible because that the longitudinal spatial and temporalspacing of the groups of charged particles permits the individualdeflection of each group. In certain embodiments, the voltage applied toeach deflection electrode stage is timed to match the velocity of eachgroup of charged particles.

Spacing between groups of charged particles can effectively provideblanking. In particular, such blanking between groups effectively usesthe full flux of a continuous or nearly continuous charged particlestream. The temporal spacing between groups allows for deflection errorcorrection (error correction signal summing can compensate- for stagedisposition, deflection aberrations, optical aberrations, and write modeprocess adjustments). Throughput improvement can be achieved bymaximizing the time that the digital beam exposes the workpiece.

In certain preferred embodiments, the digital beam is capable ofperforming a plurality of pattern exposure strategies. Such strategiesmay be designed to modify exposure dose, species, pattern quality, beamenergy per group of charged particles, beam energy for sets of groups,and beam energy for an adaptable virtual digital stencil. The apparatusmay also be capable of discretely modifying exposure dose, species,pattern quality, beam energy per group of charged particles, beam energyfor sets of groups, and beam energy for an adaptable virtual digitalstencil within a particular writing strategy to optimize that particularwriting strategy for a particular process.

In an embodiment of a writing strategy, the beam is scanned in rasterfashion across the entire area of the workpiece. In certain embodiments,the spot size of the beam is greater than the grid spacing in theraster. In certain embodiments, the spot size of the beam issubstantially equal to the grid spacing in the raster. That is, thepattern is vector scanned in the major field, vector scanned in theminor field, and raster scanned in a single pass within the feature tobe exposed. Feature processing with a digital beam can leverage the perpixel dose variation to improve feature edge quality when performingetch, implant, and deposition. In some embodiments, a digital beam spotsize to pixel ratio greater than one can average placement of the groupsof charged particles and can reduce exposure process errors. A largedigital r beam spot size to pixel ratio improves line edge roughness andallows a higher dose deposition due to cumulative dosing fromoverlapping beams. This process can also be performed with or withoutresist.

In another embodiment of a writing strategy, alternating row and columnexposure is performed with a large spot size and small pixel size ratio.Exposing alternating pixels with a digital beam produces a pixelexposure width half as wide as the selected feature, thereby increasingthe feature critical dimension over target value in both axes. That is,the pattern is vector scanned in the major field, vector scanned in theminor field, and raster scanned in alternating pixels in both x and ydirections with a single pass within the feature to be exposed.Throughput is increased by effectively reducing the number of chargedparticles per flash, but at the cost of critical dimension control.There are advantages to using this write mode for a digital beam, suchas the ability to apply per pixel dose variation or multiple speciesexposure to improve device performance, feature edge quality, andthroughput when performing resistless. etch, implant, and depositionprocesses. The throughput improvement can be dramatic since systemthroughput increases as the square of the effective writing grid. Thisprocess can be performed with or without resist.

Yet another embodiment of a writing strategy divides pixel spacedmatrices (or “composites”) and overlays exposure of a combination ofcomposites interleaved in a series of passes, with each pass offset fromother passes in both the x and y directions by a fraction of the writingaddress. That is, the pattern is vector scanned in the major field,vector scanned in the minor field, and raster scanned in a series ofpasses that interleave the pixels within the feature to be exposed. The.beam size can be set 25-100% larger than pixel size in order to averageout the flashes and to reduce the number of charged particles per group.A larger beam spot size versus pixel size helps reduce line edgeroughness by averaging systematic errors to allow a higher dosedeposition. There are advantages to using this write mode for a digitalbeam, such as the ability to apply per pixel dose variation to improvefeature edge quality when performing direct etch, implant, anddeposition processes, thereby improving feature edge quality. Thisprocess can also be performed with or without resist. The featurequality is improved, but multiple passes are achieved with little or noeffect on throughput.

Yet another embodiment of a writing strategy leverages a sampling matrixhaving an array of cells of a predetermined input address size. Eachpass produces a writing grid defined by the distance between beamplacements in a single pass. That is, the pattern is vector scanned inthe major field, vector scanned in the minor field, and raster scannedin a series of passes offset in the x and y directions to createmultiple offset composite feature patterns that interleave the pixelswithin the feature to be exposed. The composite of all passes forms theeffective exposure grid. The dose of the beam can also be freely variedwithin the operating envelope of the system. There are advantages tousing this write mode for a digital beam, such as the ability to applyper pixel dose variation to improve feature edge quality when performingresistless etch, implant, and deposition processes, thereby improvingfeature edge quality. This process can also be performed with or withoutresist with a pixel rate greater than about 400 MHz. A good balancebetween feature quality and throughput can thereby be achieved. The doseof the beam can also be varied within the process-defined operatingenvelope of the system. This can be performed with a number oftechniques including modulating the duty cycle of a beam buncher.Multiple levels of pixel intensity are provided from 0% to 100% beamintensity. Pixels of partial intensity are used along the edge of afeature so as to locate the edge between the lines of a Cartesian rasterscan grid. The dose modulation can be assigned by the user via thepattern data file. There are advantages to using this write mode fordigital beam processing, such as the ability to apply per pixel dosevariation to improve feature edge quality when performing resistlessetch, implant, and deposition processes, thereby improving feature edgequality. This process can also be performed with or without resist. Agood balance between feature quality and throughput can thereby beachieved.

FIG. 8 illustrates an example vector-raster write strategy using adigital beam. The workpiece is divided into square pixels I through 44.The beam generally writes in a serpentine motion across the workpiece,from 1 to 4, then from 5 to 12then from 13 to 22, etc. Each pixel isdivided into stripes, and each stripe is divided into fields, which aredivided into subfields. The beam generally writes in a serpentine motionacross each stripe, field, and subfield as well. Within each subfield,the beam is able to write only where written features exist. Like vectorscanning, the digital beam only scans selected areas, but the beam doesnot need to be turned off to be moved to another area, at least the timethe beam is turned off is reduced as the dead space between the groupsof charged particles can be used for that purpose.

As device geometries decrease, patterning with accurate overlay ispreferably at least one order of magnitude smaller than the minimum orcritical dimension. Workpiece processing and. handling may inducepattern errors across the workpiece that contribute to placement errors,especially as geometries fall below 0.25 microns. However, serialpatterning equipment (e.g., exposure chambers with a digital beam) hasthe flexibility to correct for these errors by registration and patterndata augmentation. A fully automated metrology program that commands thedigital beam to align itself, perform deflection/workpiece positioningcalibration, and recognize and correct for wafer pattern distortion caneliminate not only pattern defects at the most recent level, but forother pattern errors, as well.

As previously discussed, beam measurement and laser interferometersystems have accuracies to within a few angstroms. Making use of thesemeasurements, system calibration software can collect the deflectiongain, linearity, offset, and rotation for both the major and minordeflection fields. The deflection is calibrated to the laserinterferometer system, providing a well-behaved deflection motion andprofile of the digital beam within the deflection field. Linear andnonlinear errors of the digital beam profile with respect to the beamdeflection can also be measured and corrected. Because each die isregistered prior to exposure, temperature compensation can be performedby adding corrections to the pattern software and exposing that die in acorrected state, which allows the system to reduce or eliminate patterndistortions caused by annealing, vacuum radiation drain and evaporation,and improper conditioning.

The flexibility of electronic data preparation (EDP) software allowsalterations of the pattern to accommodate processing variability.Pattern editing, tone reversal, and feature biasing provide increasedflexibility to the user of the apparatus I 00. In addition, featurebordering, dose by size, and dose by type can improve digital beamassisted chemical etching (DBACE) and digital beam nucleation deposition(DBND) at small geometries.

Preferably, a data manipulation bias system corrects for pattern anddeflection distortion, for example by augmenting pattern data applyingcorrected data to the optics control system. The data manipulator systemapplies final pattern data biasing prior to optics control, andtherefore may include very fast electronics (e.g., the fastestelectronics in the system). This system sums pattern data correction,deflection distortion correction, and workpiece stage motion correctionto the front end of the optics control system. Digital to analogconverters at the front end of the optics control system convert thedigital signals from the data manipulator. Once amplified, these analogsignals drive the column 200.

Overlay accuracy can limit sub-micron lithography. For example,traditional lithography systems cannot correct for nonlinear patterndistortions caused by wafer processing, which is exacerbated byincreased workpiece sizes and reduced device geometries. However,certain digital beam systems described herein can advantageously correctfor such. errors because the pattern is not fixed on a reticle, but canchange during exposing. The adaptable virtual digital stencil is insoftcode at any given point in time. It is therefore temporally andspatially adaptable to correct in real time for nonlinear patternoffset, gain, rotation, and corrections within the minor field, whilebeing deflected in the major field. These corrections can be performedwithin features, die, or to the entire wafer.

A method of processing a workpiece 101 in the exposure chamber 102comprises exposing the workpiece 101 to a digital beam of chargedparticles. In certain embodiments, exposing the workpiece 101 comprisesforming a stream of charged particles, collimating and propagating thesteam along an axis, digitizing the stream into a digital beamcomprising groups (or packets or flashes) comprising at least onecharged particle, deflecting the groups of charged particles using aseries of deflection electrode stages disposed longitudinally along theaxis, demagnifying the pattern, and focusing the demagnified pattern ofgroups of charged particles onto the workpiece 101. The dosage ofexposure is preferably less than about 1×10¹⁷ charged particles/cm². Asdescribed above, digitizing the beam may comprise, for example, beambunching, high speed blanking, combinations thereof, and the like.

In some embodiments, deflecting the groups of charged particlescomprises selectively applying voltages across the deflection electrodesat each deflection electrode stage. Selectively applying the voltagesmay comprise applying a large voltage with a first deflection electrodestage and applying smaller voltages with other deflection electrodestages. Selectively applying the voltages may also comprise applying asmall voltage with a first deflection electrode stage and applyinglarger voltages with other deflection electrode stages. Selectivelyapplying voltages may also comprise applying approximately equalvoltages at each deflection electrode stage. Demagnification of thegroups of charged particles preferably produces packet diameters of lessthan about 200 nm, less than about 50 nm, less than about 10 nm, lessthan about 5 nm, or less than about 1 nm. The workpiece stage may movecontinuously during the exposing process. For example, the workpiecestage may move continuously over a dimension of about 100 cm over a timeperiod of 1 second. For another example, the workpiece stage may movewithout stopping for more than 5 nanoseconds per 0.5 seconds.

FIG. 5 illustrates a plurality of groups of charged particles 502, 504.In some embodiments, deflection of a group of charged particles occursduring a dead zone 512 at the workpiece such that no exposing occursduring the deflection. The rise time 509 of saturated beam pulses can beused for blank and unblank edges. In some embodiments, the geometry ofthe groups of charged particles are Gaussian in x and y dimensionsperpendicular in time, as well as Gaussian in velocity to, the axis ofpropagation. In some embodiments (e.g., as depicted in FIG. 5), thegroups of charged particles 502, 504 have a trapezoidal cross-sectionalong the longitudinal axis. In FIG. 5, two groups of charged particles502 and 504 are depicted. Each digital beam has a density distributionrise time 506 and a fall time 508. The time between no charged particlesand the peak density of charged particles is the quick pulse rise time509. The time in which each group 502, 504 has a peak density of chargedparticles is the digital flash time 510. The time between the fullconcentration of charged particles and no charged particles is the quickfall time 511. The time in which there are no charged particles is thedead zone 512 (the anti-node region). The time between the last instanceof a full concentration of charged particles in a first group, forexample the group 502, and the initial concentration of chargedparticles in a subsequent group, for example the group 504, is thedeflection time 514. The time between the first concentration of chargedparticles in a first group, for example the group 502, and the initialconcentration of charged particles for a second subsequent group, forexample the group 504, is the flash duty cycle (or “flash spot rate”)516 and is used for feature-to-feature deflection time within the minorfield. In some embodiments, however, blanking can occur over multipleduty cycles. A blanker may be used.

Referring again to FIGS. 1A and 1B, the apparatus. 100 may furthercomprise at least one dedicated process chamber 108. Additional processchambers can optionally be used for advanced processing. The processchambers 108 may comprise any variety of workpiece processing equipment.For example, and without limitation, the processing chambers 108 maycomprise etch, deposition (e.g., oxidation, nucleation, etc.), rapidthermal anneal (RTA), combinations of the same, and the like. Someprocess chambers 108 may be configured to process a workpiece 101 thathas been exposed in the exposure chamber 102, while other processchambers 108 can be configured to process a workpiece 101 before orafter processing in another process chamber 108, before processing inthe exposure chamber 108, etc. In certain embodiments, a process chamber108 does not substantively change the workpiece 101. For example, aprocess chamber 108 may comprise a calibration or metrology tool. Incertain embodiments, the apparatus 100 comprises a plurality ofprocessing chambers 108 such that a workpiece 101 may be transferredfrom a bare substrate to a substantially finished product. Preferably,workpiece 101 can be fully processed without being removed from theapparatus 100. In certain embodiments, the. duration from startingsubstrate to substantially finished product is less than one week, morepreferably less than two days, or even more preferably less than oneday, or more preferably yet in less than one hour.

In an example embodiment, two process chambers 108 are dedicated tonucleation and oxidation deposition, a third process chamber 108 isdedicated to rapid thermal annealing, and a fourth process chamber 108is dedicated to chemically-assisted digital beam etching (CADBE).Although one process chamber 108 may be adapted to perform all suchprocesses, dedication allows, for example, the use robust materials toavoid corrosion in the CADBE chamber.

Automated processing software can be used to monitor and analyze allaspects of the system's performance, to perform automation control ofall functional operations, and to optimize each process performed by thesystem. The software can perform a data gathering routine on all sensorsof the system and organize the results into operational and performancerelated reports addressing the status of the system. The software canalso prepare a processing report for each workpiece processed throughthe system including the targeted process compared to the actualprocess, which can be used to determine fault analysis and processboundaries. Feedback of the process parameters into an automated controlloop (e.g., a knowledge based routine) allows high leverage indeveloping processes. The software may incorporate data gathered fromone or more metrology processes to enhance such process development, forexample to monitor and adjust etching rates, deposition thicknesses, andcontamination. The software can preferably operate all system functions,including process sequences, process parameters for each sequence, etc.,although pattern exposure may be controlled by a pattern generationsystem. The software can produce interlocks based on the processsequences and can provide full automation and optimization of theprocesses. Other configurations are possible. User control andadjustment is also used in certain embodiments.

Etching is a process for the manufacture of semiconductor circuits. Highleverage microelectronic integrated circuits generally utilize highresolution etching of materials to within a critical dimension andlocation. The ability to etch metals, semiconductors, and dielectricswith precise control over feature depth, uniformity, anisotropy, andreproducibility is desirable for many applications. Standard processingtechniques typically utilize a resist-related patterning step followedby a wet or dry chemical etch to perform material removal.

Resist patterning limits the quality of the etch process profile, size,depth, and uniformity. Milling, or etching after exposure by a focusedion beam, provides high resolution removal of material without the useof resist. However, high dose and low sensitivity cause slow speed ofthe equipment, and milling has not been commercially successful.Chemically assisted processes (e.g., chemically assisted ion beametching (CAIBE) and reactive ion etching (RIE)) were introduced toenhance milling, but they could not be incorporated into FIB equipmentbecause the gas reacted with several components within the exposurechamber. In contrast, as described herein, low dose procedures incombination with concentrated charged particles in groups compatiblewith resistless processing provides quality patterns and highthroughput.

In certain embodiments, etch, implant, and deposition of the workpiececan be performed within the exposure chamber 102. Multiple activation byexposure to a digital beam and a process gas can dramatically improvethe efficiency of all three processes. A digital beam specificallydesigned for a particular process in terms of energy, species, andcurrent, which is possible because the digital beam parameters areadjustable, can impact and decompose a portion of the process gasmolecules. The decomposed molecules strike surface atoms of theworkpiece to sputter or implant new atoms into the workpiece, or todeposit new atoms on the workpiece surface. In some embodiments,portions and/or all of the workpiece is heated during exposing.

A new family of etching techniques is ideally suitable for highresolution, high throughput microelectronics manufacturing using aresistless process. This new process family is called digital beamassisted chemical etching (DBACE), and is up to 10 to 1.00 times moresensitive to ion exposure than milling. The process comprises at leasttwo steps including digital beam exposure of a pattern to the regions tobe etched. The target surface of a workpiece is exposed to very low doseion energy, creating a reactive region for the chemical agent. Theworkpiece is then introduced to reactive gas within a separate chamber.As a result, a high resolution dry chemical etching process activelyremoves the material within the desired location as a parallel processto digital beam pattern exposure on other workpieces within the exposurechamber. As an example, DBACE can be performed on silicon and silicondioxide (SiO₂) with chlorine (Cl₂) or fluorine (F2) gas, on galliumarsenide (GaAs) with Cl₂, on carbon (e.g., diamond) with oxygen (e.g.,O₂) and nitrous oxide (N₂O₃), on tungsten and molybdenum with carbonbromine trifluoride (CBrF₃) and high temperature superconductors (e.g.,cuprates such as La_(1.85)Ba_(0.15)CuO₄, YBa₂Cu₃O_(7-x) (yttrium bariumcopper oxide, YBCO, Y123, yttrium barium cuprate), andcuprate-perovskite ceramics with or without normal metallic regions)with wet hydroxide chemicals (e.g., sodium hydroxide (NaOH), potassiumhydroxide (KOH)). DBACE has been successfully applied to etch the gaterecesses of gallium arsenide field effect transistor (FET) deviceswithout destroying the underlying active device region.

The above description is of optional environments of use for embodimentsof methods for operating charged particle beam bunchers.

In certain embodiments, a charged particle beam buncher (e.g., spatialcharged particle beam buncher, beam buncher, buncher, etc.) includes adrift tube having a central axis, along which a plurality of ringelectrodes is provided. The plurality of ring electrodes provides a timeshifted potential gradient synchronized to the particle beam travel. Theelectric field potential is driven by a bank of RF voltage sources. Incertain embodiments, one RF voltage source is coupled to each individualring electrode within the plurality of ring electrodes, and wherein twosuch RF voltage sources generate a time varying RF electric field withinthe integral region between two adjacent ring electrodes. Theoscillating RF electric field influences motion of the particle alongthe trajectory path within the drift tube so that the particles remainbunched, funneled and filtered at the exit point of the buncher assemblyuntil hitting a desired target.

Certain embodiments include a beam buncher that incrementally alters theacceleration, velocity, and position of charged particles travelingwithin a DC (direct current) beam as they pass through a multiple numberof ring electrodes. The result of the beam buncher is to provide ahigher density distribution of charged particles with spatially resolvednodes (e.g., relatively high charged particle density) and antinodes(e.g., relatively low charged particle density) from the buncher exit totarget. The beam buncher can also provide mass selection and a laterallyresolved beam profile. In certain embodiments, the nodes have a higherparticle density than the antinodes. In certain embodiments, theantinodes have substantially zero charged particle density or zerocharged particle density. FIG. 10 schematically illustrates a chargedparticle beam formed into nodes and antinodes. In certain embodiments,the nodes and antinodes are substantially uniformly spatially resolved.The resulting beam is then bunched at high frequency with resolvedspatial distribution thus allowing improved current per beam bunch inconjunction with a high frequency of bunches per unit time. In certainembodiments, application of the beam buncher is to perform digital beamprocessing of semiconductor materials, machining of materials, digitalmedia disks, communications, biomedical research and alterations,process and development, ion thrusters, spacecraft propulsion andattitude control, beam weapons applications and surveillanceapplications. Targets can include a detector, wafer, media disk, tissuesample, military target, freespace, atmosphere, machined component, etc.

Temporal bunchers operate to collect charged particles, which arespatially dispersed along one or more axes and bring them closertogether later in time at a specific drift distance. However, beyondthis time focus, without additional means being applied to a group oflike charge particles to keep them confined, the space chargeinteractions may generate sufficient Coulomb repulsion forces to causethe charged particles in the bunch to once again disperse. Applicationsof temporal charged particle bunchers include time of flight massspectrometers and microwave power amplifiers.

A typical temporal buncher includes two spaced apart parallel flat plateelectrodes. The two flat plate electrodes create an electric field thatis substantially uniform between the plates. Each electrode includes anaperture through the plate thickness which charged particles may pass.The aperture can be near the center of the electrode. In use, a group ofcharged particles drift along an axis extending between the electrodesthrough the aperture in each electrode. Each electrode is initially heldat a first potential. The value of the electrical potential of one ofthe electrodes can then be rapidly adjusted by means of a high-speedswitch. This generates an electric field between the plates. Theelectric field can be used to speed up or slow down charged particlesmoving between the plates relative to the DC beam velocity (e.g.,“velocity modulation”) causing charged particle to bunch.

The RF potential of a temporal buncher can be changed in less time thanthe time for the charged particles to travel between the electrodes. Bychanging the RF potential in less time than the time for the chargedparticles to travel between electrodes, this effectively provides eachcharged particle, during the bunching period, with slightly differentintegrated acceleration profiles depending upon when the chargedparticle enters the excitation gap and the initial phase of the RFfield. Consequently, when a group of such charged particles bunchtogether, the AC (e.g., alternating current) velocity spectrum of thegroup due to the RF modulation may contain components related to thefundamental bunching frequency as well as higher order harmonics. As aresult, the charged particles in the group may exhibit oscillations intheir position back and forth relative to the center mass of each bunchas the bunch travels. If the space charge forces are not ignored, thecavity location of the maximum RF beam current is not a function ofsignal level, gap width, or the frequency spectrum of operation. Theoscillations created by a temporal buncher reduce the ability to controlindividual charged particles.

For applications like digital beam semiconductor processing, biomedicalradiation therapy, spacecraft ion thrusters and attitude controlsystems, advanced material machining methods, telecommunications,defense related critical technologies, etc., a steady stream of uniformspatially distributed charged particle pulses would be beneficial atbunching modulation frequencies ≥50 MHz so that the pulses of chargedparticles can be deflected or manipulated in some controlled fashiondownstream of the charged particle buncher and become bunched usinglower energies for more efficient operation.

In certain embodiments, the time varying electric field between adjacentelectrodes is quasi-electrostatic, so that each of the charged particlesin a group traveling through the buncher experiences a relativelyconstant phase simulating a traveling wave propagating through thebuncher at a phase velocity equal to the mean DC beam velocity. Incertain embodiments, each charged particle in a group experiences adifferent phase of the electric field depending upon the time of arrivalof the charged particle into the spatial buncher. Moreover, eachparticle traveling through the spatial buncher experiences either acorresponding phase of the applied electric field or the oppositepolarity electric field at 180° difference in phase. In certainembodiments, the charged particles experiences one phase travelingthrough the first half of the spatial buncher and 180° difference inphase traveling through the second half of the spatial buncher.

Certain embodiments provide a steady and/or segmented stream ofspatially uniform bunches from the exit of an apparatus until the beamhits a desired target. Certain embodiments include the ability tomanipulate and control the combination of multiple gaps per each relatedbeam wavelength by allowing every charged particle to be displaced byits own unique fixed phase of a traveling electric field. The field canbe reversed in partial segmentation or full segmentation throughouttravel allowing equivalent or close to equivalent adiabatic energyinput. For example, the first half of the series of electrodes can be atan opposite voltage as the second half so that energy put into thecharged particles by the first half is removed by the second half. Incertain embodiments, the application is applied to moderate to highenergy particle beams ranging between 500 keV to 500 MeV or greater than500 keV. In certain embodiments, the beam bunch current is below 10nano-Amp per beam bunch, above 1 nano-Amp per beam bunch, or greaterthan 10 milliAmp per beam bunch. In certain embodiments, with bunchingfrequencies are between 1 GHz to 10 THz, greater than 1 GHz or greaterthan 10 GHz. Advantageously, lower input voltage can be used byutilizing more electrode plates at lower voltage. In certainembodiments, the deflection of each beam bunch can be performed afterexiting the apparatus but prior to target impact.

In certain embodiments, a spatial charged particle buncher includes aseries of spaced apart electrodes separated from each other by adistance. Each electrode includes an aperture through the platethickness which charged particles may pass. The beam buncher may includea stack of plates, rings or wire loop electrodes. In certainembodiments, the aperture is near the center of the electrode. Theplates can have a perimeter through which charged panicles may pass. Incertain embodiments, each electrode has a single aperture through whichcharged particles are transmitted in use. In certain embodiments, theaperture is substantially circular.

In certain embodiments, the spatial charged particle buncher includes afirst electrode, one or more intermediate electrodes and a lastelectrode. The intermediate electrodes are between the first electrodeand the last electrode. In certain embodiments, the spatial chargedparticle buncher includes a series of at least 10, 50, 100, 300, 500,1,000, 3,000, 10,000, 100,000, 1,000,000 or 10,000,000 electrodes. Incertain embodiments, the spatial charged particle buncher includesbetween 100 electrodes, and 10,000 electrodes. In certain embodiments,the electrodes include plates having apertures through which chargedparticles may pass. In certain embodiments, the electrodes are evenlyspaced apart. In certain embodiments, the distance between electrodes isat least 10 times less or at least 20 times less than the distance equalto the DC beam velocity times the bunching period. In certainembodiments, the electrodes are substantially flat and/or circular. Theelectrodes can also be concave, convex or hyperbolic. In certainembodiments, the surface of the aperture is tapered. For example, theelectrode interacting surface within the aperture is tapered. Thesurface of the aperture can also be straight walled, bow tie, etc., asillustrated in FIG. 16.

FIG. 9 illustrates an example of a spatial charged particle buncher 900with a plurality of electrodes 902 with apertures 904 according tocertain embodiments. FIG. 11 schematically illustrates aquasi-electrostatic simulation of the electric field distributionthrough a section of an embodiment of a spatial charged particle buncherat a single instance in time. The arrows represent the electric field102 between the electrodes 1104. Each of the electrodes 1104 has anaperture 1106 through it.

In certain embodiments, an AC or RF voltage waveform of variableprofile, is applied to each electrode using a suitable voltage network,distribution or ladder circuit. An example of an embodiment of a voltageladder 1000 is schematically illustrated in FIG. 15. The voltage ladder1000 includes voltage sources 1004, transmission lines 1008, threegroups of two electrodes 1002, and a capacitor 1010 and a resistor 1006between each set of two electrodes 1002.

In certain embodiments, an RF impulse generator producing a periodicsequence of variable amplitude and variable shape voltage pulses areapplied to each electrode. In certain embodiments, in operation, theperiodic pulses (e.g., periodic pulse train) or triangular voltagewaveform of a series of voltage steps is applied to each electrode inthe buncher. The voltage waveform can be a series of periodic linearpiecewise continuous voltage steps, or a series of variable amplitudeand variable shape voltage pulses. The initial on time of the start ofthe periodic voltage waveform can be temporally delayed from electrodeto electrode. In certain embodiments, the time delay between when thevoltage waveform is applied to each electrode in sequence is (i) by atime interval equal to the charged particle transit time betweenadjacent electrodes, (ii) by a harmonic of the time interval equal tothe charged particle transit time between adjacent electrodes, (iii) bya halftone of the time interval equal to the charged particle transittime between adjacent electrodes, and/or (iv) by a time less than orequal to the inverse of the bunching frequency. In certain embodiments,the frequency of the periodic applied electrode voltage waveform is (i)equal to the bunch frequency, (ii) a harmonic of the bunch frequency, or(3) a mixed-mode signal of the bunch frequency.

In certain embodiments, the electric field is shaped such that chargedparticles traveling through the buncher and having the same mass tocharge ratio are all brought substantially into time focus at the targetplane downstream of the buncher. In certain embodiments, the electricfield causes spatial alignment of charged particles such that the massof charged particles is filtered by positional displacement. In certainembodiments, the profile of the electric field is a sawtooth triangularprofile.

In certain embodiments, the voltage range applied to each adjacentelectrode is increased or decreased in steps. In certain embodiments,the steps are substantially constant. In certain embodiments, the aboutfirst half of the series of electrodes of the spatial charge buncher canbe increased in steps of about 0.001 to 1000 volts, about 1 volt, about5 volts, or about 10 volts. In certain embodiments, the voltages appliedto the about latter half of the spatial charge buncher are decreased insteps of about 0.001 to 1000 volts, about 1 volt, about 5 volts, orabout 10 volts. In certain embodiments, the number of discrete periodicvoltage steps or voltage pulses applied to each electrode is (i) greaterthan or equal to 3 discrete components, (ii) greater than or equal to 5discrete components, (iii) greater than of equal to 7 discretecomponents, (iv) greater than or equal to 9 discrete components, (v)greater than or equal to I 0 discrete components, or (vi) greater thanor equal to 20 discrete components.

In certain embodiments, the first and last electrodes of the series ofelectrodes are connected to ground to act as field termination platesfor the buncher device. For example, the first and last electrodes canbe connected to means for transferring charge onto or off the electrode.In certain embodiments, the time varying electric field between eachadjacent pair of electrodes is tuned to be matched to the time varyingelectric field between any other two adjacent plates except for beingdisplaced in phase.

FIG. 13 illustrates a quasi-electrostatic simulation result of theperiodic axial variable amplitude electric field pulse train produced inthe excitation gap between two adjacent electrodes formed by applying aperiodic train of variable amplitude voltage pulses to each electrodewith the voltage signals delayed between two adjacent electrodes by adelay equal to the charged particle transit time through the regiondefined between two adjacent electrodes. FIG. 14 illustrates aquasi-electrostatic simulation result of the periodic stepped axialelectric field synchronized with the charged particle beam travel sothat every charged particle experiences a constant phase of the periodicstepped axial electric field as it propagates down the axis of thedevice from excitation gap-to-excitation gap. Each of the five plotsrepresents the voltage as a function of time for a series of fiveelectrodes.

In certain embodiments, the time varying electric field, driven at thebunching modulation frequency, is generated between two successiveelectrodes in the spatial buncher. In certain embodiments, the bunchingmodulation frequency and or the node repetition rate is above 1 MHz,above 10 MHz, above 50 MHz, above 100 MHz, above 250 MHz, above 1 GHz,above 10 GHz, or above 100 GHz. In certain embodiments, the bunchingmodulation frequency is below 100 GHz. The first, intermediate and lastelectrodes can be connected in series alternately with capacitors,network, an active circuit and/or an active component. In certainembodiments, the electrodes are connected in series with resistors. Thecapacitors may be connected in parallel with resistors chosen to allow aproportionally small conduction current to flow between the electrodesto allow any free charges to drain from the plates, and may notsubstantially affecting performance of the buncher. The shape of thetime varying electric field generated can be varied. For example, theshape can be varied by the capacitance between each pair of adjacentelectrodes.

The shaped of the electric field can be generally approximated byMaxwell's displacement field with free conduction currents beingtransferred on to or away from the first, intermediate, and lastelectrodes. The speed with which the shaped displacement field can begenerated and/or adjusted can be generated and/or adjusted by themagnitude of the current flowing to or from the first, intermediate, andlast electrodes. Electronic switches using field effect transistors cansustain high switching currents of in excess of 100 Amperes making itpossible to apply a potential of a few volts in less than a nanosecond.

In certain embodiments, the magnitude of displacement current flowingonto or away from the intermediate electrodes exceeds any conductioncurrent flowing onto or off the intermediate electrodes by at least twoorders of magnitude, more preferably at least three orders of magnitude.

In certain embodiments, the DC beam current is less than 100 nano-Ampsper bunch, less than 500 nanoAmps per bunch, less than I milli-Amps perbunch, less than I 00 milli-Amps per bunch, less than 1 Amps per bunchor less than 100 Amps per bunch. In certain embodiments, the DC beamcurrent is greater than 10 nano-Amps per bunch or greater than 100nano-Amps per bunch.

According to certain embodiments, the transit time of charged particlesbetween two electrodes is less than or equal to 200 ns, less than orequal to 10 ns, less than or equal to 5 ns, less than or equal to 50 ps,or less than or equal to 0.1 ps.

In certain embodiments, the spatial buncher is maintained at a pressureof greater than or equal to 0.000001 mbar, greater than or equal to0.00005 mbar, greater than or equal to 0.0001 mbar, greater than orequal to 0.005 mbar, greater than or equal to 0.01 mbar, greater than orequal to 0.05 mbar, greater than or equal to 0.1 mbar, greater than orequal to 0.5 mbar, greater than or equal to 1 mbar, greater than orequal to 5 mbar, or greater than or equal to 10 mbar. In certainembodiments, the spatial buncher is maintained at a pressure of lessthan or equal to 10 mbar, less than or equal to 5 mbar, less than orequal to 1 mbar, less than or equal to 0.5 mbar, less than or equal to0.1 mbar, less than or equal to 0.05 mbar, less than or equal to 0.01mbar, less than or equal to 0.005 mbar, less than or equal to 0.001mbar, less than or equal to 0.0005 mbar, or less than or equal to 0.0001mbar. In certain embodiments, the spatial buncher is maintained at apressure of between 0.0001 and 10 mbar, between 0.0001 and 1 mbar,between 0.0001 and 0.1 mbar, between 0.0001 and 0.01 mbar, between0.0001 and 0.001 mbar, between 0.001 and 10 mbar, between 0.001 and 1mbar, between 0.00,1 and 0.1 mbar, between 0.001 and 0.01 mbar, between0.01 and 10 mbar, between 0.01 and 1 mbar, between 0.01 and 0.1 mbar,between 0.1 and 10 mbar, between 0.1 and 1 mbar, or between 1 and 10mbar.

In certain embodiments, the spatial buncher includes a charged particlefunnel that includes a plurality of electrodes having apertures thatbecome progressively smaller or larger as charged particles pass throughthe apertures. In certain embodiments, the plurality of electrodes are aseries of electrodes and the apertures become progressively smaller orlarger through the series. The spatial buncher configured as a chargedparticle funnel may have different voltage schemes, such as DC, AC, RF,or a combination thereof, applied to each of the electrode. The chargedparticle funnel may include a stack of plate, ring, or wire loopelectrodes.

In certain embodiments, the diameter of the apertures of at least 50%,60%, 70%, 80%, 90% or 95% of the electrodes forming the spatial buncheris less than or equal to 2 mm, less than or equal to 1 mm, less than orequal to 0.5 mm, less than or equal to 0.2 mm, or less than or equal to0.1 mm. In certain embodiments, at least 50%, 60%, 70%, 80%, 90% or 95%of the electrodes forming the spatial buncher have apertures withsubstantially the same size and/or area. In certain embodiments, thethickness of at least 50%, 60%, 70%, 80%, 90% or 95% of the electrodesis less than or equal to 3 mm, less than or equal to 2.0 mm, less thanor equal to 1.0 mm, less than or equal to 0.5 mm, less than or equal to0.1 mm, or less than or equal to 0.01 mm.

In certain embodiments, the spatial charged particle buncher has alength of less than 5 cm, 5-10 cm, 10-15 cm, or greater than 15 cm. Incertain embodiments, at least 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%,90%, or 95% of the electrodes are connected to an AC and/or RF voltagesupply in combination with a DC voltage source.

In certain embodiments, axially adjacent electrodes are supplied with ACand/or RF voltages that are in exact or similar phase with each other.Transmission delay lines tuned to the transit time of charged particlestraveling between two adjacent electrodes can be used to insure thateach particle experiences a constant phase of the time varying electricfield as it travels through the first half of the spatial buncher andthe inverse polarity with 180 degree phase difference while travelingthrough the second half of the spatial buncher. In certain embodiments,the charged particles traveling through the spatial buncher experiencesseveral such control segments of alternating electric field phase. Incertain embodiments, each charged particle traveling through the spatialbuncher experiences at least 2 such cycles, at least 5 such cycles, orat least a thousand such cycles. In certain embodiments, each cycle isbalanced in polarity such that the beam experiences the same or almostsimilar number of positive and negative electric fields.

A repeating pattern of electrical DC potentials may also be superimposedalong the length of the spatial buncher so that a DC periodic waveformis formed to provide additional operational capability as a chargedparticle guide. The DC potential waveform can be arranged to travelalong the charged particle guide in the direction and at a velocity atwhich it is desired to move charged particles along the spatial buncher.The charged particle guide may also be configured to act as a chargedparticle funnel wherein adjacent ring electrodes have successivelysmaller apertures with increasing radial electrostatic field density tosqueeze down the radial extent of the charged particle bunches andimprove the resolution for digital beam processing. In certainembodiments, the radial shaped electric field is generated substantiallysuch that, in use, the electric field causes the position of chargedparticles to be displaced radially to the direction of propagation whilecreating an axial time varying electric field that causes a steady orsegmented substantially uniform spatial distribution of chargedparticles that form nodes of relatively high particle density andantipodes of relatively low particle density.

In certain embodiments, the spatial buncher may include an AC or RFcharged particle guide such as a multiple rod set or stacked ring set,which is segmented in the axial direction so that independent transientDC potentials may be applied to each segment. The transient DCpotentials can be superimposed on top of the RF confining voltage andany constant DC offset voltage. The DC potentials can be changedtemporally to generate a travelling DC potential wave in the axialdirection.

At any instant in time, a voltage gradient can be generated betweensegments that act to adiabatically push or pull charged particleslongitudinally either in the forward or backward direction related tothe interacting field. As the DC voltage gradient moves in the samedirection as the beam trajectory, the field applied to the chargedparticles forces displacement. The individual DC voltages on each of thesegments may be programmed to create a specific waveform. Furthermore,the individual DC voltages on each of the segments may be programmed tochange in synchronism so that the DC potential waveform is maintainedbut shifted in the direction to displace the charged particles forwardor backward along the path of travel.

The DC potential waveform may be superimposed on any nominally imposedconstant axial DC voltage offset. In certain embodiments, a non-constantaxial DC voltage gradient can be used. The travelling DC wave may beprovided in conjunction with an axial DG voltage gradient.

The transient DC voltage applied to each segment may be above or belowthat of a constant DC voltage offset applied to the electrodes formingthe charged particle guide. The transient DC voltage causes the chargedparticles to move in the axial direction. The transient DC voltagesapplied to each segment may be programmed to change continuously or in aseries of steps. The sequence of voltages applied to each segment mayrepeat at regular intervals or at intervals that may progressivelyincrease or decrease.

After the beam has passed through the series of electrodes, the chargedparticle beam can pass through a means for deflecting charged particles.For example, the charged particle beam can pass through one or moredeflection electrodes, one or more magnetic lenses, one or morereflective optics, one or more focusing optics, etc. The chargedparticles can exit in a substantially continuous or pseudo-continuousmanner.

A charged particle source can precede the series of electrons. Chargedparticle sources can include ion sources, pulsed ion sources, positivelycharged ions, negatively charged ions, singly charged ions, doublycharged ions, multiple charged ions, positrons, electrons, carbonnanotubes, liquid metal ion sources, plasma ion sources, volume plasmaion sources, gas field ionization sources, carbon nanotube fieldemitters, free electron lasers, pulsed ablation ion sources,magnetically confined plasma anode sources, thermal field emissionelectron sources, sources adapted to generate a plurality of chargedparticle species, etc.

Although this invention has been disclosed in the context of certainpreferred embodiments and examples, it will be understood by thoseskilled in the art that the present invention extends beyond thespecifically disclosed embodiments to other alternative embodimentsand/or uses of the invention and obvious modifications and equivalentsthereof. In addition, while several variations of the invention havebeen shown and described in detail, other modifications, which arewithin the scope of this invention, will be readily apparent to those ofskill in the art based upon this disclosure. It is also contemplatedthat various combinations or sub-combinations of the specific featuresand aspects of the embodiments may be made and still fall within thescope of the invention. It should be understood that various featuresand aspects of the disclosed embodiments can be combined with, orsubstituted for, one another in order to form varying modes of thedisclosed invention. Thus, it is intended that the scope of the presentinvention herein disclosed should not be limited by the particulardisclosed embodiments described above, but should be determined only bya fair reading of the claims that follow.

1. A charged particle bunching system comprising: a series of electrodesarranged to generate a shaped electric field, the series comprising afirst electrode, a last electrode and one or more intermediateelectrodes; and a waveform device attached to the electrodes andconfigured to apply a periodic potential waveform to each electrodeindependently in a manner so as to form a quasi-electrostatic timevarying potential gradient between adjacent electrodes and to spatiallydistribute charged particles propagating along the series of electrodesto form a charged particle beam comprising a plurality of nodes andantinodes, wherein the nodes have a charged particle density and theantinodes have substantially no charged particle density.
 2. The systemof claim 1, further comprising a magnetically confined ion sourceconfigured to provide the charged particles to the electrodes.
 3. Thesystem of claim 1, wherein the electrodes comprise apertures withtapered surfaces, the apertures configured to allow the chargedparticles to pass through the electrodes.
 4. The system of claim 1,further comprising a deflector comprising electrode deflection stagesdisposed longitudinally along an axis of the charged particle beam. 5.The system of claim 1, further comprising a deflector comprisingmagnetic deflection stages disposed longitudinally along an axis of thecharged particle beam.
 6. The system of claim 1, further comprising adeflector comprising a deflector lens configured to demagnify the nodes.7. The system of claim 1, further comprising an objective lensconfigured to demagnify and focus the nodes.
 8. The system of claim 1,further comprising a stage configured to continuously move a workpiecewhile the workpiece is exposed to the charged particle beam.
 9. Thesystem of claim 1, wherein the charged particle beam is configured to beapplied to a workpiece for biomedical research and alterations.
 10. Thesystem of claim 1, wherein the charged particle beam is configured to beapplied to a workpiece.
 11. The system of claim 1, wherein the chargedparticle beam is configured to provide spacecraft propulsion.
 12. Thesystem of claim 1, wherein the charged particle beam is configured to beapplied onto surveillance targets.
 13. The system of claim 1, whereinthe charged particle beam is configured to be applied in open space fordata transfer communications.
 14. The system of claim 1, wherein thecharged particle beam is configured to interact with electromagneticradiation that applies a pulsed incident neutralizing beam to thecharged particle beam.
 15. The system of claim 14, wherein theelectromagnetic radiation comprises a pulsed laser beam.
 16. The systemof claim 1 where the charged particle beam has a current greater than 1nanoamp per node.
 17. The system of claim 1, wherein the chargedparticle beam has a total beam current greater than 1 milliamp.
 18. Acharged particle collimator comprising: a beam buncher in operativecommunication with a source of charged particles; a deflector configuredto receive the charged particles; and an objective lens assemblyconfigured to receive the charged particles from the deflector, theobjective lens comprising a lens, a mirror, and reflective andrefractive optic lenses configured to demagnify, focus, and deflectgroups of the charged particles received from the deflector to aworkpiece.
 19. The collimator of claim 18, wherein the beam buncher isconfigured to apply a pulsed laser beam to the charged particle source.20. The collimator of claim 18, wherein the beam buncher is configuredto modulate an on/off state of the charged particle source.
 21. Thecollimator of claim 18, further comprising an aperture configured toshape the charged particle beam.
 22. The collimator of claim 18, whereinthe beam buncher is configured to deflect individual groups of thecharged particles in a direction substantially perpendicular to an axisof propagation of the charged particle beam.